I second the possibility that it could be a plantar wart and suggest you have it diagnosed by a doctor. I had a plantar wart as a kid. I don't remember anything at all about it except having my foot injected at the doctors. I remember which part of my foot was being injected and it is right where you mention.

The GP had a look, took a scalpel to it and said if it comes back have a go at it with a pumice stone.

He didn't know what caused the irritation but suggested that I might have had a splinter or something ages ago that caused an irritation, the callus formed over the sore spot and the wood is absorbed by the body but the skin deposits remain to irritate for ever and ever and ever (or until you take a sharp knife to them to slice them off)

Well there is a less severe option. There's the heel cream called eulactal. It softens the skin so that it washes off in the shower. Normally if you want to fix your heels you have to apply it twice a day for about two weeks - depending on how bad they are.

Don't buy the gold i don't think its got any more urea in it. But this stuff does work. Although of course more expensive than those methods you referred to.